Question

What is the mass defect of lithium? Assume the following:
Atomic number of lithium = 3
Atomic mass of lithium = 7.0144 atomic mass units.
Mass of 1 proton = 1.0073 atomic mass units.
Mass of 1 neutron = 1.0087 atomic mass units.
A.
0.0043 atomic mass units
B.
0.0423 atomic mass units
C.
3.0219 atomic mass units
D.
4.0348 atomic mass units
E.
7.0567 atomic mass units

Answer 1

To calculate the mass defect of lithium, we can follow these steps:

1. **Determine the number of protons and neutrons in lithium:**
- The atomic number of lithium is 3, which means it has 3 protons.
- Since the atomic mass of lithium is approximately 7, we can estimate the number of neutrons by subtracting the number of protons from the atomic mass:
\[
\text{Number of neutrons} = \text{Atomic mass} - \text{Number of protons} = 7 - 3 = 4
\]

2. **Calculate the mass of the nucleons (protons and neutrons):**
- Mass from protons:
\[
\text{Mass of protons} = (\text{Number of protons}) \times (\text{Mass of 1 proton}) = 3 \times 1.0073 = 3.0219 \text{ atomic mass units}
\]
- Mass from neutrons:
\[
\text{Mass of neutrons} = (\text{Number of neutrons}) \times (\text{Mass of 1 neutron}) = 4 \times 1.0087 = 4.0348 \text{ atomic mass units}
\]
- Total mass of the nucleons:
\[
\text{Total mass of nucleons} = 3.0219 + 4.0348 = 7.0567 \text{ atomic mass units}
\]

3. **Calculate the mass defect:**
- The mass defect is the difference between the total mass of the nucleons and the actual atomic mass:
\[
\text{Mass defect} = \text{Total mass of nucleons} - \text{Atomic mass of lithium}
\]
\[
\text{Mass defect} = 7.0567 - 7.0144 = 0.0423 \text{ atomic mass units}
\]

Based on this calculation, the mass defect of lithium is:

**B. 0.0423 atomic mass units**